This proposal concerns studies of the retina as a model system of biochemical control. Glutamine Synthetase (GS) and other enzymes, and their possible relation to vision and general retinal metabolism are a major focus. Previous studies showed 1) structural requirements of steroid for GS induction; 2) improved GS assay; 3) GS induction in retinoblastoma derived cells; 4) GS is not confined to single retinal cell type; 5) enhancement of cortisol induction of GS by Actimonycin-D; 6) normal early development of GS in retinas of mice with inherited retinal degeneration; 7) retina has active GS activity which may be separable from glutamyl transferase activity. Current studies concern 1) effects on induction of GS and subsequent control of the enzyme by substrate and product; 2) necessity of presence of inducer for continued GS synthesis; 3) uptake of hormone by retinal tissue under various conditions; 4) other metabolic phenomena in the retina.